1. Technical Field
The present invention relates to a liquid supply apparatus which supplies liquid, particularly to a liquid supply apparatus including a diaphragm pump.
2. Related Art
There is an ink jet printer in which an ink cartridge is arranged on a main body side of the printer and ink is supplied to a recording head of the ink jet printer from the ink cartridge through an ink supply path. In such a printer, a supply pump such as a diaphragm pump is arranged on the ink supply path so as to pressure-supply ink to the recording head side from the ink cartridge side by applying a pressure to the ink (for example, JP-A-2006-272661).
In general, when the diaphragm pump is driven by supplying a negative pressure to the diaphragm pump, a spring biasing the diaphragm is contracted with the negative pressure, and the diaphragm abuts against a stopper so that ink is sucked into an ink chamber containing ink. After the negative pressure is released, the diaphragm is pressurized only by the biasing force of the spring so that the ink in the ink chamber is pressurized and supplied.
However, there are variations in environment of usage of the printer and errors in manufacturing the diaphragm pump. Therefore, the negative pressure supplied to the diaphragm is not constant. Accordingly, when the negative pressure supplied to the diaphragm is larger than a predetermined pressure, the diaphragm is also expanded with the negative pressure after the diaphragm abuts against the spring so that the diaphragm stops at a position where the diaphragm balances with the supplied negative pressure. As a result, when ink is supplied by releasing the negative pressure, a supply pressure of the ink is increased. This causes a risk that the ink supply path at a joint portion or the like may be damaged. Further, a variation in the supply pressure of ink is generated.